As described in Patent Literatures 1 and 2, a conventional ultrasonic diagnostic apparatus transmits ultrasonic into an object, receives the ultrasonic reflection echo signal of a living organ from the reflected wave, performs signal processing on the signal to produce and display a monochrome section image (B mode image) of a diagnostic part having intensities as the ultrasonic reflectivities.
Patent Literature 2 has disclosed a technique involving performing three-dimension coordinate conversion from the monochrome section image and its taking position to obtain three-dimensional volume data including a plurality of section image data items arranged three-dimensionally and then performing volume rendering thereof to provide a monochrome three-dimensional image of a diagnostic part viewed from an arbitrary direction of line of sight. A disclosed technique of the rendering includes providing an opacity for each of voxels constituting the three-dimensional volume data in accordance with the value of the intensity of the voxel, sequentially accumulating the intensity values of the voxels on the line of sight until the accumulated value of the opacities of the voxels arranged on the line of sight reaches one, and using the accumulated intensity value as a pixel value on a two-dimensional projection plane.
Patent Literatures 1 and 2 have also disclosed a technique of determining an elasticity image of a diagnostic part. First, two frames of the monochrome section image are selected, block matching or the like is performed to determine the displacement of each point on the image between the two frames, the determined displacement is subjected to known calculations to determine the elasticity value (such as strain and coefficient of elasticity) representing the hardness for each point on the image. The magnitude of the determined elasticity value is converted into hue information based on a color conversion table to obtain the two-dimensional elasticity image representing the elasticity value as the hue.
In addition, Patent Literature 2 has disclosed a technique in which, in order to solve the problem of being incapable of obtaining a three-dimensional image of an inner lesion portion hidden by outer voxels having high opacities in a three-dimensional gray-scale image, an opacity is provided for each of voxels in three-dimensional volume data obtained from the monochrome section image in accordance with the magnitude of the elasticity value to perform volume rendering. This can provide the three-dimensional gray-scale image showing a hard organ more opaquely and a soft organ more transparently.
In Patent Literature 2, a plurality of two-dimensional elasticity images are coordinate-converted into three-dimensional volume data which is then subjected to volume rendering to produce a three-dimensional elasticity image. In the typical rendering method in which voxel values are simply accumulated, a problem occurs in which the elasticity values are accumulated to provide the three-dimensional elasticity image including distorted elasticity characteristics of a living organ, so that the intensity data of the monochrome section image is used to determine the voxel having the highest contribution on the line of sight, and the elasticity value of that voxel is used as the elasticity value of the two-dimensional projection plane to produce the three-dimensional elasticity image.
For the display method, the monochrome section image (two-dimensional) and the two-dimensional elasticity image are displayed one on the other in Patent Literature 1. In Patent Literature 2, the monochrome three-dimensional image and the three-dimensional elasticity image are superimposed into one image which is then displayed together with the monochrome section images in three directions on one screen.
Patent Literature 3 has disclosed displaying a monochrome section image and a two-dimensional elasticity image together on one screen and superimposing and displaying the monochrome section image on the two-dimensional elasticity image.